This disclosure relates to a method of fabricating zinc oxide (ZnO) thin films.
ZnO, which is a II-IV Group oxide, is a semiconductor substance having a hexagonal wurtzite crystal structure and a wide optical energy band gap of about 3.3 eV. ZnO thin film has a strong piezoelectricity and photoelectric effect. Thus the optical characteristics of ZnO thin films are similar to those of GaN used as a material for the conventional UV/blue light-emitting diodes (LEDs) and laser diodes (LDs). Especially, ZnO thin film is known to have advantageous characteristics. For example, it has an excitation binding energy three times higher than GaN at room temperature, thus resulting in more efficient emission. Also, ZnO thin film has a low threshold energy for stimulated spontaneous emission by laser pumping. In addition, ZnO thin film has excellent transmittance in the infrared and visible light regions, electrical conductivity, and durability to plasma, and its raw material cost is economical. Therefore, the application range of ZnO thin films is very wide, for example, TFTs, transparent electrodes by doping, photocatalysts, energy saving coating materials for window glasses, acousto-optic devices, ferroelectric memories, solar cells, or reduction gas detection sensors.
Techniques for growing the ZnO thin films include various coating methods such as a chemical vapor deposition, metal organic chemical vapor deposition, organometallic chemical vapor deposition, molecular beam deposition, organometallic molecular beam deposition, pulse laser deposition, atomic layer deposition, sputtering, RF magnetron sputtering, or the like. However, the equipment for carrying out these methods are expensive and their operations are not very simple. Moreover, when growing the ZnO thin films at high temperatures, the substrate underneath may be stressed by the high temperature.
In the preparation of a precursor solution of ZnO thin film, Zn acetate, Zn chloride, Zn nitrate and the like are used as a Zn supplier. In this case, the decomposition temperature (generally, 500° C. or higher) of these Zn suppliers is high. Thus, it is difficult to apply these Zn suppliers to a device for a flexible substrate or a glass substrate for a transparent electrode.